The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Modern aircraft operate at altitudes at which there is insufficient oxygen to sustain normal human conscious activities. At high altitudes, pressurized aircraft cabins or cockpits are typically provided with a cabin pressurizing and ventilating system that maintains an environment equivalent to standard atmospheric pressure at an elevation of approximately 8,000 feet. The environmental equivalent altitude is referred to as “cabin altitude.” Since the relative proportion of oxygen in earth's atmosphere is relatively constant, regardless of altitude, a satisfactory aircraft cabin environment is maintained simply by taking in atmospheric air from outside the aircraft and compressing it. In cabin pressurizing and ventilating systems, fresh pressurized air is supplied to the cabin or cockpit from an air pressure source, such as using engine bleed air, or by using a separate air pump, supercharger, auxiliary power unit (APU) or the like, to draw in atmospheric air. Air pressure within the cabin is maintained at the required pressure by controlling the flow of air out of the cabin through one or more outflow valves in the aircraft.
For emergency conditions, however, a supply of oxygen is needed. In military aircraft, such as fighter aircraft, the pilot or pilots are permanently supplied by an on-board oxygen generating system (commonly abbreviated to OBOGS), using a zeolite-type molecular sieve to separate gases from the air. In commercial aircraft, zeolite-type oxygen generation systems can also be used to provide emergency oxygen for the passengers and crew. If cabin pressure is lost, or the cabin environment or air supply is contaminated in some way (e.g. by smoke or other toxins), oxygen masks can be deployed for use by the aircraft crew and passengers until such time as the aircraft descends to a safe altitude (e.g. below 10,000 feet) and/or the cabin contamination problem is resolved through venting, etc. While failures of emergency oxygen systems are relatively rare, they are still possible. In the event of such a failure, persons using the system can be quickly overcome by hypoxia and other dangerous conditions. Engine bleed system or APU contamination or failure also present possible avenues for contamination of emergency air or loss of sufficient oxygen.
Unfortunately, many aircraft are not provided with a backup oxygen supply in case of such failure. For example, many systems do not have an independent, pristine backup oxygen supply. On the other hand, in some systems the backup oxygen may be charged by the primary on-board oxygen-generating system, and thus can contain the same contaminants. Additionally, while some systems provide oxygen and pressure sensors, these systems often depend on crew action, and do not automatically engage. In military aircraft, the pilot and crew will normally have an oxygen mask donned at high altitude, but may not notice a signal from an oxygen performance monitor, particularly during a combat situation when their attention is directed elsewhere. In such cases, where an oxygen mask is normally worn, contamination of the oxygen supply can very rapidly affect pilot performance and safety. Additionally, in some cases crew action may be limited to a quick descent that could cause back pressure on the system at low engine settings, which can hinder its performance.
The present disclosure is directed toward one or more of the above-mentioned issues.